This invention relates to tagging macro-organisms in order to facilitate research on the macro-organisms. More particularly, the invention relates to the injection into a macro-organism of a magnetized tag severed from a supply of wire and incrementally advanced to an implanting device.
U.S. Pat. No. 3,820,545 to Jefferts discloses a method and apparatus for implanting such tags. The tags are injected into macro-organisms in an unmagnetized state and subsequently magnetized in place for later detection. U.S. Pat. Nos. 3,128,744 and 3,313,301 issued to Bergman and Jefferts disclose earlier related prior art systems. The '744 patent discloses a small magnetically coded tag, while the '301 patent is directed to an instrument for implanting such tags.
FIG. 1b illustrates a prior art magnetizer of the kind for magetizing tags after implantation. A tagged specimen is guided, in the direction indicated by an arrow 154, through a permanent magnet toroid 150 having a downstream magnetic flux shield 152 usually made of soft iron. The shield 152 is necessary to prevent demagnetization of the tag as the fish in which the tag is implanted passes out of the magnetizing field.
One alternative to magnetizing a tag inside the organism is to reduce the size of the magnetizer and install it around the injection needle, so that the magnetizer works to magnetize the tag before implantation. FIG. 1a shows an unsatisfactory permanent magnet toroid 160 for accomplishing such a magnetization subsequent to implantation. A fringing field 162 has a direction opposite to the direction of a primary field 164 in a transverse plane passing through the geometric center of the toroid. As a result a tag magnetized by the primary field tends to become demagnetized by the fringing field upon passage of the tagged fish beyond the toroid. This approach has the additional shortcoming that the magnetizer magnetizes both the tag and the wire with the consequence that the tag is attracted to the wire and may be accidentally extracted from the specimen as the needle and wire are withdrawn after tagging.
An object of the present invention is to provide an improved method and apparatus of the above-described type wherein a tag is magnetized prior to injection into a macro-organism.
Another object of the present invention is to provide an improved method and apparatus for forming a magnetized tag and injecting the tag into a macro-organism.
Another, more particular, object of the present invention is to provide such an improved method and apparatus wherein magnetic attraction between a magnetized tag and an injecting wire is eliminated to prevent of the tag from a macro-organism upon completion of an implantation operation.